Abstract

We proposed and demonstrated a simple but deterministic scheme for generating polarization-entangled photon pairs at telecommunication wavelengths with type-II quasi-phase-matched spontaneous parametric down-conversion (QPM-SPDC) having two poling periods. We fabricated a LiNbO3 crystal having two poling periods so as to generate entangled photons at two wavelengths, i.e., 1506 nm and 1594 nm. We characterized the two-photon polarization state with state tomography and confirmed that the state was highly entangled.

Two-period quasi-phase-matched device. The crystallographic axes of the lithium niobate crystal are referred to as x, y, and z. The pump (o-ray), signal (o-ray), and idler (e-ray) beams propagate collinearly along the x axis, having linear polarizations along y, y, and z, respectively.

Results of the polarization correlation measurement. Circles are the measured coincidence counts as a function of θ2 while θ1 was fixed at 0° or 90° in (a), ±45° in (b). The curves are calculated by Eqs. (10) and (11).